Auto merge of #51527 - kennytm:do-not-auto-hide-inherent-impl, r=GuillaumeGomez

Don't auto-hide inherent impls even if `rustdoc-collapse == true`.

This PR changes the auto-collapse behavior when a page is first loaded:

* Inherent impls will never be collapsed by default (new behavior).
* Trait impls will always be collapsed by default, same as before.
* Other items are collapsed according to localStorage, same as before.

This should be much more useful since there is no hint what the content of a collapsed inherent impl would be (try to collapse everything in https://doc.rust-lang.org/std/vec/struct.Vec.html and guess where a method like `try_reserve` or `splice` would be).

Manually clicking the global [-]/[+] will still collapse/expand everything.